   <!-- 2.html结构 -->
   <div id="app">
    <input type="text" v-model="message" @keyup.enter="getMessage" />
    <input type="button" v-model="message" @click="setMessage" />
    <h3>{{message}}</h3>
 </div>
  <!-- 1.开发环境版本，包含了有帮助的命令行警告 -->
  <script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
  <!-- 3.创建Vue实例 -->
  <script>
      var app=new Vue({
          el:"#app",
          data:{
            message:"沙丁鱼"
          },
          methods:{
              getMessage:function(){
                  alert(this.message)
              },
              setMessage:function(){
                  this.message="酷丁鱼";
              }
          }
      })
  </script>
